The watching sports world learned something Saturday, and it may well be worth bearing in mind during the weeks ahead: Andrew Luck is not, and never has been, Peyton Manning.

Since Andrew Luck was drafted by the Indianapolis Colts with the No. 1 draft pick in the 2012 National Football League draft, the comparisons have been almost too easy. So, naturally, everyone made them. They were No. 1 draft picks, they ate up playbooks like Cheerios and milk, they were the sons of pro quarterbacks themselves, and, of course, Luck was drafted to replace Manning.

Yet Saturday afternoon, even as Luck was leading the Indianapolis Colts to a 45-44 comeback victory of Manningian proportions over the Kansas City Chiefs, there was little doubt that this was not Peyton Manning behind center. And never was that more apparent than on the "Luck Fumble."

It is rare that a fumble can define a quarterback's career. And yes, Luck's career is nowhere near being defined yet. His second season is (preposterously) not even finished yet. But when Colts running back Donald Brown fumbled at the 2 yard line with the Colts down 41-31 with 10:31 remaining in the fourth quarter – having clawed back from a 38-10 deficit only 16 minutes earlier – fortune took an unforgettable bounce, right into Luck's hands.

What Luck did next was as instinctive as it was instructive: He lowered his shoulder and barreled headfirst into the endzone. Given the stakes, probably any quarterback would have done the same. But for Luck, the moment seemed a cosmic calling card of who he is as a football player.

Both Luck and Manning are extraordinary quarterbacks and are in that way similar. But for Manning, each game is a palette for perfection. When everything goes perfectly – when he throws seven touchdowns in a game, as he did this year, for instance – there is something clockwork about it. His genius is in setting impossibly high standards for himself and then reaching them with unearthly consistency.

You know he is going to beat you. You do everything imaginable to stop him. And he still beats you just the way he wants to.

But Saturday was the perfect portrait of the quarterback Luck is becoming. Yes, like Manning, he can run the no-huddle offense to perfection, carving up a defense with his decisionmaking and pinpoint passing, as he did on the first drive of the game.

He can throw three interceptions. He can be down 38-10 and look lost. He can rocket passes yards over receivers' heads.

Yet when that happens, it's entirely possible that he's just getting started.

In Manning's second year, a three-interception game would no doubt have given us "Peyton Manning face" – that lip-locked grimace that tells you (without even looking at the scoreboard) that all is not going according to plan. In his second year, Luck gave a glimpse of what "Andrew Luck face" looks like.

"Guys like him are just wired differently,'' Colts quarterbacks coach Clyde Christensen told Sports Illustrated. "He just keeps playing. No matter what. There are a lot of quarterbacks, when they throw three interceptions, they're scared to throw the ball after that."

"Not this guy. This guy gets mad at himself, and you see his eyes get focused and he says, 'We are going to go on a drive, right now.' That's just a rare quality. Lot of guys shrink back and go, 'Oh, boy. I don't want to make another mistake.' But this guy takes his anger and aggression and makes something good happen."

If Manning is the ultimate perfectionist, then Luck is developing into the ultimate competitor. He is part Manning genius, part Brett Favre gunslinger, part Aaron Rodgers improvisationalist, and part Ben Roethlisberger beast of human being. But he is also part lunk-headed fullback, plowing headfirst heedlessly to score a touchdown. When another Colts running back, Trent Richardson, fumbled in the second quarter, Luck tackled the Chiefs linebacker who scooped it up.

In that moment of instinct, Luck is fearless. That is how he could lead the Colts to the second-largest playoff comeback in league history with 4-1/2 minutes to spare. Of all the remarkable facts of Saturday's game, perhaps the most amazing is that the Colts were in a position to kill off the last two minutes of the game despite have been down 28 points early in the third quarter.

During a week when Luck faces a showdown with one of the two greatest quarterbacks of this generation – either Manning in Denver or Tom Brady in New England – that is worth bearing in mind.